1. Field of the Invention
This invention relates to a dual carburetor used for fuel supply or a two-cylinder engine and, more particularly, to a dual carburetor with compact-structured main fuel passages and low-speed fuel passages.
2. Description of the Related Art
Duel carburetors, in particular, duel side-flow carburetors with horizontally extending two parallel intake passages, are widely used in two-cylinder outboard engines or stationary engines because they need no particular consideration on appropriate distribution of a fuel upon being mounted in a two-cylinder engine.
In dual carburetors, in general, independent main fuel passages and low-speed fuel passages are provided for respective air suction passages, as shown in U.S. Pat. No. 3,188,060, for example.
FIG. 7 is a diagram illustrating, in particular, the construction of passages in a conventional dual carburetor of this type. Two air suction passages 53, 53 extend in parallel in horizontal directions above a float-type fuel chamber 51. Choke valves 54 are attached to a single choke valve rod 55 extending across two air suction passages 53, 53. Similarly, throttle valves 56 are attached to a single throttle valve rod 57 extending across two air passages 53, 53.
Main fuel passages 59, 59 for two air suction passages 53, 53 are located at opposite sides of a float 52 in the fuel chamber 51. These main fuel passages 59 are branched from a delivery passage 58 opening at the bottom of the fuel chamber 51, then extend substantially upwardly along opposite sides of the float 52. Each of the main fuel passages, 59, has a main jet 60, emulsion tube 61, and main nozzle 62. A main air bleed tube 63 for each main fuel passage 59 extends horizontally from near its inlet along the bottom, and then slopes down to the emulsion tube 61. A main air bleed jet 64 is provided at the inlet of each main air bleed passage 63.
Similarly, two low-speed fuel passages 65, 65 are provided for two air suction passages 53, 53. Each low-speed fuel passage 65 is branched from each main fuel passage 59 between the main jet 60 and the emulsion tube 61, first extends vertically outside each air suction passage 53 and then runs horizontally to near the throttle valve 56. Each low-speed fuel conduit 65 has a slow jet 66 and an emulsion tube 67 in its vertical portion, and a slow port 68, as a low-speed port, and an idle port 69 at the terminal end of its horizontal portion. A low-speed air bleed passage 71 is provided for each low-speed fuel passage 65. Each low-speed air bleed passage 71 extends from near the inlet of the air suction passage 53 first horizontally above it and then vertically outside it to the emulsion tube 67. A low-speed air bleed jet 72 is provided at the inlet of each low-speed air bleed passage 71.
As to the construction of passages for the main fuel systems including the main fuel passages 59 and the main air bleed passages 63 and the construction of passages for the low-speed fuel systems including the low-speed passages 65 and the low-speed air bleed passages 71, the main fuel passages 59 have a very simple construction, namely, they extends substantially straight from the bottom of the fuel chamber 51 along one side thereof.
However, the main air bleed passages 63, low-speed fuel passages 65 and low-speed air bleed passages 71 have portions extending horizontally, diagonally and vertically. Especially the low-speed fuel passages 65 and the low-speed air bleed passages 71 turn several times and form complex shapes as a whole. It is very difficult or, at least, troublesome to make these complex forms by drilling for respective turn or curve portions and to reliably seal a number of end apertures used for inserting a drill. These factors have heretofore disturbed improvements in production efficiency and production cost.